// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Security.Claims;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http.Authentication;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Http.Features.Authentication;
using Microsoft.Extensions.Primitives;
using Newtonsoft.Json.Linq;
using System.Threading;

namespace Microsoft.AspNetCore.Authentication.OAuth
{
    public class OAuthHandler<TOptions> : RemoteAuthenticationHandler<TOptions> where TOptions : OAuthOptions
    {
        public OAuthHandler(HttpClient backchannel)
        {
            Backchannel = backchannel;
        }

        protected HttpClient Backchannel { get; private set; }

        protected override async Task<AuthenticateResult> HandleRemoteAuthenticateAsync()
        {
            AuthenticationProperties properties = null;
            var query = Request.Query;

            var error = query["error"];
            if (!StringValues.IsNullOrEmpty(error))
            {
                var failureMessage = new StringBuilder();
                failureMessage.Append(error);
                var errorDescription = query["error_description"];
                if (!StringValues.IsNullOrEmpty(errorDescription))
                {
                    failureMessage.Append(";Description=").Append(errorDescription);
                }
                var errorUri = query["error_uri"];
                if (!StringValues.IsNullOrEmpty(errorUri))
                {
                    failureMessage.Append(";Uri=").Append(errorUri);
                }

                return AuthenticateResult.Fail(failureMessage.ToString());
            }

            var code = query["code"];
            var state = query["state"];

            properties = Options.StateDataFormat.Unprotect(state);
            if (properties == null)
            {
                return AuthenticateResult.Fail("The oauth state was missing or invalid.");
            }

            // OAuth2 10.12 CSRF
            if (!ValidateCorrelationId(properties))
            {
                return AuthenticateResult.Fail("Correlation failed.");
            }

            if (StringValues.IsNullOrEmpty(code))
            {
                return AuthenticateResult.Fail("Code was not found.");
            }

            var tokens = await ExchangeCodeAsync(code, BuildRedirectUri(Options.CallbackPath));

            if (tokens.Error != null)
            {
                return AuthenticateResult.Fail(tokens.Error);
            }

            if (string.IsNullOrEmpty(tokens.AccessToken))
            {
                return AuthenticateResult.Fail("Failed to retrieve access token.");
            }

            var identity = new ClaimsIdentity(Options.ClaimsIssuer);

            if (Options.SaveTokens)
            {
                var authTokens = new List<AuthenticationToken>();

                authTokens.Add(new AuthenticationToken { Name = "access_token", Value = tokens.AccessToken });
                if (!string.IsNullOrEmpty(tokens.RefreshToken))
                {
                    authTokens.Add(new AuthenticationToken { Name = "refresh_token", Value = tokens.RefreshToken });
                }

                if (!string.IsNullOrEmpty(tokens.TokenType))
                {
                    authTokens.Add(new AuthenticationToken { Name = "token_type", Value = tokens.TokenType });
                }

                if (!string.IsNullOrEmpty(tokens.ExpiresIn))
                {
                    int value;
                    if (int.TryParse(tokens.ExpiresIn, NumberStyles.Integer, CultureInfo.InvariantCulture, out value))
                    {
                        // https://www.w3.org/TR/xmlschema-2/#dateTime
                        // https://msdn.microsoft.com/en-us/library/az4se3k1(v=vs.110).aspx
                        var expiresAt = Options.SystemClock.UtcNow + TimeSpan.FromSeconds(value);
                        authTokens.Add(new AuthenticationToken
                        {
                            Name = "expires_at",
                            Value = expiresAt.ToString("o", CultureInfo.InvariantCulture)
                        });
                    }
                }

                properties.StoreTokens(authTokens);
            }

            var ticket = await CreateTicketAsync(identity, properties, tokens);
            if (ticket != null)
            {
                return AuthenticateResult.Success(ticket);
            }
            else
            {
                return AuthenticateResult.Fail("Failed to retrieve user information from remote server.");
            }
        }

        protected virtual async Task<OAuthTokenResponse> ExchangeCodeAsync(string code, string redirectUri)
        {
            var tokenRequestParameters = new Dictionary<string, string>()
            {
                { "client_id", Options.ClientId },
                { "redirect_uri", redirectUri },
                { "client_secret", Options.ClientSecret },
                { "code", code },
                { "grant_type", "authorization_code" },
            };

            var requestContent = new FormUrlEncodedContent(tokenRequestParameters);

            var requestMessage = new HttpRequestMessage(HttpMethod.Post, Options.TokenEndpoint);
            requestMessage.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            requestMessage.Content = requestContent;
            var response = await Backchannel.SendAsync(requestMessage, Context.RequestAborted);
            if (response.IsSuccessStatusCode)
            {
                var payload = JObject.Parse(await response.Content.ReadAsStringAsync());
                return OAuthTokenResponse.Success(payload);
            }
            else
            {
                var error = "OAuth token endpoint failure: " + await Display(response);
                return OAuthTokenResponse.Failed(new Exception(error));
            }
        }

        private static async Task<string> Display(HttpResponseMessage response)
        {
            var output = new StringBuilder();
            output.Append("Status: " + response.StatusCode + ";");
            output.Append("Headers: " + response.Headers.ToString() + ";");
            output.Append("Body: " + await response.Content.ReadAsStringAsync() + ";");
            return output.ToString();
        }

        protected virtual async Task<AuthenticationTicket> CreateTicketAsync(ClaimsIdentity identity, AuthenticationProperties properties, OAuthTokenResponse tokens)
        {
            var ticket = new AuthenticationTicket(new ClaimsPrincipal(identity), properties, Options.AuthenticationScheme);
            var context = new OAuthCreatingTicketContext(ticket, Context, Options, Backchannel, tokens);
            await Options.Events.CreatingTicket(context);
            return context.Ticket;
        }

        protected override async Task<bool> HandleUnauthorizedAsync(ChallengeContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            var properties = new AuthenticationProperties(context.Properties);

            if (string.IsNullOrEmpty(properties.RedirectUri))
            {
                properties.RedirectUri = CurrentUri;
            }

            // OAuth2 10.12 CSRF
            GenerateCorrelationId(properties);

            var authorizationEndpoint = BuildChallengeUrl(properties, BuildRedirectUri(Options.CallbackPath));
            var redirectContext = new OAuthRedirectToAuthorizationContext(
                Context, Options,
                properties, authorizationEndpoint);
            await Options.Events.RedirectToAuthorizationEndpoint(redirectContext);
            return true;
        }

        protected virtual string BuildChallengeUrl(AuthenticationProperties properties, string redirectUri)
        {
            var scope = FormatScope();

            var state = Options.StateDataFormat.Protect(properties);

            var queryBuilder = new QueryBuilder()
            {
                { "client_id", Options.ClientId },
                { "scope", scope },
                { "response_type", "code" },
                { "redirect_uri", redirectUri },
                { "state", state },
            };
            return Options.AuthorizationEndpoint + queryBuilder.ToString();
        }

        protected virtual string FormatScope()
        {
            // OAuth2 3.3 space separated
            return string.Join(" ", Options.Scope);
        }
    }
}